In recent years the use of active deviation control tools in the drill string bottom hole assembly has been commonplace. Whether to cause deliberate well bore deviation or to prevent unwanted deviation, elements of the down hole assembly are commonly used for the control purpose. Selective placement of stabilizers can sometimes be used by the skillful driller but results at best are somewhat uncertain. Rigid bent subs can be used above drilling motors, or within the motor body. These are not active in that the bend cannot be controlled from the surface but when used with down hole steering instruments to control rotational orientation they are reliable with the application of moderate driller skill and experience. Active deflection tools can be supplied to apply lateral force on the well bore wall to deflect the bit but these tools tend to be complicated and, hence, tend to be troublesome. Active tools to deflect the drill string centerline at a pivot point can be about the most simple of the active class. Adding the ability to operate as a straight tool or a deflected tool by choice of the driller at the surface adds little to the complexity and it is that tool to which this invention is directed.
It is therefore an object of this invention to provide apparatus responsive to the manipulation of the rate of flow of drilling fluid through the drill string to selectively cause the drill string centerline to deviate near the drill head of a down hole assembly.
It is another object of this invention to provide apparatus for use in the drill string near the drill head to respond to selected manipulation of the drilling fluid flow to maintain the centerline of the drill string in a straight configuration.
It is yet another object of this invention to provide apparatus near the drill head to respond to repeated selected manipulations of the drilling fluid flow rate to change the down hole assembly between bent and straight configuration each time the flow rate is selectively manipulated.
It is still a further object of this invention to provide a drilling fluid pressure signal, detectable at the surface, to indicate which configuration exists down hole.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.